Medical containers filled with drug solutions, blood, or the like require transparency in order to check changes due to contamination by impurities or blending of drug solutions, heat resistance to withstand sterilization treatment, flexibility to facilitate dispensing of drug solutions, gas barrier properties to suppress degeneration or a decrease in quality of drug solutions and the like due to permeation of water vapor or oxygen into the container, reduced fine particle elution from the container (low occurrence of fine particles), and the like.
Conventionally, glass containers have been used as medical containers having satisfactory performance with regard to these requirements. However, since there are problems such as container damage due to impact or being dropped and contamination due to infiltration of external gas into the container during administration of the drug solution, plastic containers which have excellent impact resistance, are flexible, and facilitate dispensing of the contents have come to be used. For such plastic containers, soft vinyl chloride resin, ethylene-vinyl acetate copolymer resin, polypropylene resin, and polyethylene resins such as high-pressure low-density polyethylene, linear low-density polyethylene, and high-density polyethylene have been used. However, soft vinyl chloride resin has problems in hygiene such as the plasticizer eluting into the drug solution, ethylene-vinyl acetate copolymer resin has the problem of lacking heat resistance, and polypropylene resin has problems in flexibility and cleanliness (low occurrence of fine particles). Furthermore, polyethylene resins have the problems that heat resistance, gas barrier properties, and the like decrease if the density is lowered to achieve satisfactory transparency and flexibility and cleanliness may further deteriorate.
Linear polyethylene produced with a single-site type catalyst having excellent transparency has been recently developed, and methods for solving the above problems by laminating film that uses it as a raw material have been proposed (refer to Patent Documents 1 to 3). However, transparency is still insufficient in these laminates, and the impact strength of the heat seal portion and the like of a molded container is not considered sufficient, and therefore improvements have been desired.
Additionally, a method has been proposed for obtaining a container in which deformation and wrinkling do not occur even after sterilization treatment at 121° C. and the strength of the seal portion is excellent by laminating an inner layer, an intermediate layer, and an outer layer constructed from material containing a polyethylene resin having certain physical properties (refer to Patent Document 4). Although this method certainly makes it possible to retain high seal strength even after sterilization treatment, it does not solve the problem that container transparency decreases after sterilization treatment, and improvements have been desired.
Additionally, a method has been proposed wherein a laminate for an infusion bag having heat resistance capable of withstanding sterilization at 124° C. is obtained by blending a certain amount of a crystal nucleus agent in an intermediate layer disposed between an outer layer and an inner layer (refer to Patent Document 5). However, even this method still does not solve the problem that transparency decreases due to sterilization treatment.